Process of case hardening



Patented Dec. 22, 1931 UNITED STATES PATENT OFFICE AUGUSTUS B. KINZEL, 0F BEECHHIIRST, NEW YORK, ASSIGNOR TO ELECTED METAL- LURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA I PROCESS OF CASE HARDENING No Drawing. Application filed May 26,

My inventionrelates to the production of nitrided layers on metals by heating the metals in nitrogen-containing agents, such as ammonia. It has particular reference to an improved method of forming such hard wear-resistant cases.

The object of my invention is to provide means for accelerating and intensifying the action of nitridinggases on metal articles so as to reduce the time required to produce a case of given hardness or thickness.

The case hardening of alloys is useful as a means of forming hard wearing surfaces on articles to be used for various machine and tool parts. In order to avoid the formation of brittle cases or cause any other deleterious effect upon the material being treated the nitriding process is preferably carried out at low temperatures. To permit the production of a satisfactory case at temperatures of the order of 460 C. to 580 C. it is often customary to alloy with the material to be treated small amounts of a promoting agent such as aluminum or vanadium. A heating period of from 12 to 20 hours in a nitriding atmosphere such as ammonia is usually required to form a suitable case, the length of time of treatment increasing with a decrease in temperature. Such prolonged heating which has been necessary to insure a proper reaction is expensive. I

I have found that hard, nitrogen-containing cases may be produced in much less time by irradiating the nitriding gas and preferably also the surface of the specimen being treated with ultra-Violet energy. Such energy may be generated by any of the common and convenient forms of electric arcs such as the carbon are or the quartz mercury vapor arc.

In the preferred form of my invention the specimen to be treated is placed in a chamber containing ammonia gas or other suitable nitriding agent. One side of the chamber may be provided with a window of quartz glass or other material transparent to ultra-violet energy through which the nitriding atmosphere may be irradiated from a, source outside the chamber. In this manner the specimen may be so placed that its surface is ex- 1930. Serial No. 455,955.

ahard nitride case may be formed on a specimen in four hours by means of my invention, whereas a similar specimen W111 show no hardening Whatever when treated in the abscence of ultra-violet energy for the same length of time. It is also possible to form a case in a given length of time, for instance 12 to 24 hours, with the use of ultra-violet radiation the depth of which is approximately twice that formed under-similar conditions without such radiation.

It is very probable that the nitriding gas, such as ammonia, is dissociated to a certain extent when exposed to ultra-violet radiation forming a more active form of gas which causes the nitriding reaction. to take place more readily. It also appears that the action of ultra-violet energy on the surface of the specimen being treated is a further contributing factor in accelerating the formation of a hardened case although I am unable to explain why this should be so. I have found for instance that when the nitriding atmosphere only is irradiated and the metal surface of the specimen is shielded from the direct radiation some improvement results, but when the specimen is also exposed the speed of the nitriding reaction is much greater.

The invention should not be restrlcted by the foregoing attempt to describe the theoryinvolved. It will be evident that various modifications in the method as described may be made without departing from the spirit of my invention as defined in the appendedseaaaa said nitriding agent to ultra-violet radiation 2. The method of nitriding metal articles Which comprises heating the articles in the presence of a nitriding agent and irradiating said articles While in said atmosgshere with ultra-violet energy.

3. The method of nitridirig me'tai articles which comprises subjecting the heated arti. cles to an atmosphere of ammonia in a chain her, and irradiating said atmosphere with ultra-violet energy from a source outside said chamber.

4. The method of ni'triding metal articles Which comprises heating the articles in chamber containing an atmosphere of ammo nia and subjecting said atmosphere and surface of said articles to ultra-Violet radia leion through a portion of said, chamber trans parent to ultra-violet energy.

In testimony whereof, E afiiz; my signature.

AUGUSTUS B. KHNQEL 

